21105505638 has 40 divisors (see below), whose sum is σ = 54047964432. Its totient is φ = 6030144144.

The previous prime is 21105505637. The next prime is 21105505643. The reversal of 21105505638 is 83650550112.

It is a happy number.

21105505638 is a `hidden beast` number, since 2 + 1 + 10 + 5 + 5 + 0 + 5 + 638 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105505637) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 9304645 + ... + 9306912.

Almost surely, 2^21105505638 is an apocalyptic number.

21105505638 is an abundant number, since it is smaller than the sum of its proper divisors (32942458794).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21105505638 is a wasteful number, since it uses less digits than its factorization.

21105505638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18611578 (or 18611569 counting only the distinct ones).

The product of its (nonzero) digits is 36000, while the sum is 36.

The spelling of 21105505638 in words is "twenty-one billion, one hundred five million, five hundred five thousand, six hundred thirty-eight".